In a small-scale wireless network system supposed to be used mainly in a building facility and in a home such as a sensor network system, a technique has been developed that measures the position of a wireless communication terminal with high precision.
Since a GPS (Global Positioning System) signal cannot be received in the building facility and in the home, a system is known that measures a distance and a distance difference among a plurality of terminals to estimate the position using a time of arrival (TOA) of radio waves from a base station whose position is known, a time difference of arrival (TDOA) of radio waves, and a radio wave receiving intensity.
An assumption is made that coordinates of a base station are known in advance in the above. In order to save time and effort to set coordinates of the base station, a technique is proposed such that “at least (N+1) base stations (N=1 to 3) and positioning servers are provided. The distances among at least (N+1) base stations are calculated. Relative coordinates of each base station are obtained. The obtained relative coordinates are evaluated. A switching to the terminal positioning processing for obtaining the position of the terminal is judged. The position of the terminal is obtained using a propagation time of the wireless signal that is transmitted and received between the terminal and the base station and relative coordinates among the obtained base stations.”
On the other hand, in a wireless communication system in which a number of terminals are installed for buildings and homes in general, since an output is suppressed so as to be able to be driven by batteries, causing a limit in a communication range to be from approximately several meters to several tens of meters.
As a result, like ZigBee (trademark), for example, a multi-hop network technique is known that enables communications in a wider area in which an intermediate communication terminal relays data for terminals to which no radio waves can reach directly.
In recent years, in buildings and factories, sensors are installed at various locations and an environment measurement system is employed that measures environmental conditions such as temperature, humidity, and luminance in order to properly control air conditioning and lighting apparatuses. For example, in an air conditioning system, an air conditioning apparatus is controlled such that the measurement value of a temperature sensor installed at the air supply opening and the remote controller of the indoor unit of the air conditioning apparatus becomes a set temperature.
Further, in order to carefully control the apparatus according to the request by residents and the temperature distribution of the space, and to precisely evaluate energy performance of the building, environmental conditions need to be measured at more measurement points.
In order to measure environmental conditions at a number of measurement points, in general, a number of sensors need to be installed at a number of places by increasing the number of sensors to be measured. Therefore, increase in cost and complicated management become challenges.
In relation to the above environment measurement, as a technique intended “to improve precision and accuracy of plant diagnosis and reduce variations in inspection by making the sensor to be self-advancing to obtain a number of process values at many points in order to measure the facility in the plant and process values of the area”, such a technique is proposed that “a sensor detects the facility constituting a plant or a process value of a predetermined area. The sensor is provided with drive means that moves to a desired position in the facility or a predetermined area to detect process values.” (Patent Literature 2)    Patent Literature 1 Japanese Unexamined Patent Application Publication No. 2007-248362    Patent Literature 2 Japanese Unexamined Patent Application Publication No. 2003-130695